Current communication systems that switch according to the time division multiplex method, in particular narrowband switching equipment, are connected with one another via individual narrowband fixed connections or narrowband line bundles. Narrowband connections represent in particular PCM-oriented connections, that is, digitized telephone connections or connections that transmit digital information with a transmission speed of up to 64 kbit/s. Narrowband line bundles are formed through multiplexing of the message and signaling information of several narrowband connections, whereby standardized line bundles comprise 24 or 30 narrowband connections and a transmission speed of 1544 kbit/s or 2048 kbit/s. The signaling for the multiplexed narrowband connections is transmitted in an additional narrowband connection, generally known as a central signaling channel. The individual narrowband connections or line bundles provided between the communication systems are switched via fixed connections provided by public or private network operators.
In the future, communication networks operating according to the asynchronous transfer mode (known to those skilled in the art as ATM communication systems) are provided for the switching or, respectively, transmission of the message and signaling information of line bundles in particular. For this purpose, it has been proposed in the relevant standardization committee (ATM Forum) in a CES (circuit emulation service) standard to insert the combined message and signaling information of line bundles into cells and to switch them transparently via permanent virtual connections of an ATM communication network. The cells provided for a switching in a communication network comprise a cell head (header) having 5 bytes, and a use part (payload) having 48 bytes. The message information to be switched is inserted into the payload using intermediate memories. The header contains in particular the routing information, the virtual channel and path information and the call reference number. Using the routing information, the cells are switched via the ATM communication systems of the ATM communication network. A switching of individual narrowband connections from a line bundle via the ATM communication network to different communication systems is not provided.